Drill bit seals

ABSTRACT

An earth boring drill employing roller cutters is provided with a new and improved seal to inhibit ingress of detritus into the cutter bearing area and egress of lubricant therefrom. The parts may be so arranged that when assembled, the seal is placed in hoop compression. The shape of the seal is such that its cross section is not overly compressed or displaced when in operating position: this prevents undue compression set, wear and heating of the seal. Also, the seal has a greater radial cross-sectional extent that axial extent by a ratio of at least one-and-one-half to one to conserve bearing space and to provide the necessary flexibility to accommodate the various movements of the cutter relative to the shaft upon which it is rotatably mounted.

United States Patent [1 1 Murdoch et a1.

[ Oct. 16, 1973 DRILL BIT SEALS [75] Inventors: Henry W. Murdoch; PercyW.

' Schumacher, Jr., both of Houston,

Tex.

[73] Assignee: G. W. Murphey Industries, Inc.,

Houston, Tex.

[22] Filed: Aug. 2, 1972 [21] Appl. No.: 277,351

[52] US. Cl 175/371, 175/228, 308/8.2 [51] Int. Cl. E211) 9/08, F16j15/16 [58] Field of Search 175/371, 372, 228;

[56] References Cited UNITED STATES PATENTS 3,047,344 7/1962 Gros175/371 UX 2,676,790 4/1954 Turner 308/82 X 2,814,465 11/1957 Green308/82 3,397,928 8/1968 Galle 308/361 X 3,467,448 9/1969 Galle 175/372 X3,656,764 4/1972 Robinson 175/371 X Primary ExaminerDavid H. BrownAttorney-C. M. Kucera [5 7] ABSTRACT An earth boring drill employingroller cutters'is provided with a new and improved seal to inhibitingress of detritus into the cutter bearing area and egress of lubricanttherefrom. The parts may be so arranged that when assembled, the seal isplaced in hoop compression. The shape of the seal is such that its crosssection is not overly compressed or displaced when in operatingposition: this prevents undue compression set, wear and heating of theseal. Also, the seal has a greater radial cross-sectional extent thataxial extent by a ratio of at least one-and-one-half to one to conservebearing space and to provide the necessary flexibility to accommodatethe various movements of the cutter relative to the shaft upon which itis rotatably mounted.

11 Claims, 3 Drawing Figures PATENTEDnm 16 Ian 3.765%95 SHEET 2 or 2BACKGROUND The present invention relates to earth boring drill bits ofthe roller cutter type and more particularly to improvements in sealmeans therefor to confine a lubricant in the bearing area interiorly ofthe cutter and to keep formation cuttings and other detritus out of suchbearing area.

During drilling operations, the seal encounters fluctuations in positionand fluid pressure since the drill bit operates at various depths in awell in which drilling fluid is employed, and the cutter movement iscomplex relative to its bearing shaft in that it includes rapid axialand radial as well as wobbling motions, the magnitudes of which changeas the parts are worn. Thus, a drill bit seal should operate undervarious conditions of operation and wear if it is to be effective toprotect the bearings and enhance the useful drilling life of the bit.Also, it is desired that the seal take up as little axial space aspractical so that adequate bearing capacity remains.

The seal of the invention is an elastomeric packing type seal which isshaped and arranged to be particularly useful as a rotary or dynamicseal for use in rock bit roller cutters.

Other shapes and arrangements of elastomeric packing type seals havebeen used in rock bit cutters in which, for example, the seal may be inthe form of an O ring, or the seal might be approximately square incross section. Packing type seals usually have solid cross sections andare single piece seals made of a single material, unlike lip seals orseals made of more than one material.

Seal manufacturers have recommended that for rotary applications, an Oring seal, for example, should be compressed in cross section less thanpercent to prevent undue compression set, fatigue, wear and heating ofthe seal. For rock bit applications, the clearances and movementsbetween the parts may be quite large so that the seal in order to beeffective must be compressed sufficiently to be able to bridge suchclearances between the cutter and its shaft as they occur. This mayindicate that the seal should be compressed in cross section more than10 percent because for an O ring having a cross-sectional diameter of0.139 inches, a 10 percent squeeze would be only approximately 0.014inches whereas the cutter movement toward and away from its shaft may begreater than 0.014 inches. But simply to compress the seal more than 10percent may result in compression set and the other seal problems aspreviously stated.

It would seem that a solution would be to use an O ring having a largecross-sectional diameter such that the percent compression would besmall while the total compression of the ring would be sufficient totake care of the expected cutter excursions; however, in rock bits thespace available is very limited and to use such rings would result inless room for the bearings, so this would not be a practical solution.

It is an object of this invention to provide a seal which has a greaterradial cross-sectional extent than axial extent by a ratio of at leastone-and-one-half to one so that the total radial compression ordisplacement of the seal cross section can be sufficient to provide forthe clearances and movements of the cutter with respect to its shafttaking into account additional clearances resulting from hearing wear.It is believed that in bits of say approximately nine inches indiameter, the seal cross section should be compressed at least 0.25inches.

Since the seal cross section has a larger radial than axial extent, thecompression thereof may be less than ten percent and still provide thedesired excursion to effectively seal the cutter bearings withoutincurring undue compression set and the other attendant problemspreviously discussed.

Further, the seal shape leaves room for adequate cutter bearingcapacity.

SUMMARY In the practice of this invention, there is provided a seal,preferably rectangular in cross section, between a drill bit cutter andits bearing shaft, the parts being arranged and sized so that the sealunder operating conditions is generally in hoop or circumferentialcompression rather than in hoop tension.

DRAWINGS FIG. 1 is a longitudinal sectional view through a drill bitroller cutter together with its associated bearing shaft and supportillustrating a seal arrangement constructed in accordance with thisinvention.

FIG. 2 is a partial side elevation view of the seal of the invention. I

FIG. 3 is a sectional view taken along line 33 in FIG. 2.

DESCRIPTION Referring to the drawings, there is shown at 10 a conecutter type of earth drill of generally conventional constructioncomprising a bit head 11 and a threaded shank 12 for connection to adrill stem (not shown). A

cutter support 13 extends downwardly from the bithead and a bearingshaft 14 extends downwardly and inwardly from the support 13.

A roller cutter 15 is rotatably mounted on the bearing shaft 14 onfriction bearings 16 and 17 and ball bearings 18. After the ballbearings have been inserted into place, a retaining pin 19 serves tokeep them in place. The cutter 15, shaft 14, support 13 and attendantparts may be made of alloy steel and the cutter 15 may have tungstencarbide cutting inserts 20 therein, or other suitable cutting elements.

The cutter 15 has a groove 21 extending radially outwardly from thebearing shaft 14, and a seal ring 22, which may be made of Buna-N or thelike and may be generally rectangular in cross section, is disposed ingroove 21. A flange portion 23 helps to confine and protect the outboardside of seal ring 22 from being damaged by detritus or formationcuttings. The groove 21 serves to confine the seal 22 so that it doesnot tip or tilt axially to any great extent, moreover the groove finishmay be relatively rough since it is preferred that the seal ring rotatewith the cutter 15 and slide upon the bearing shaft 14.

A grease reservoir 24 in bit head 11 serves to provide lubricant to thecutter bearing through aperture 25 and passageway 26 in the bit head 11and support 13 and channels 27 and 28 in the retaining pin 19. Thereservoir 24 has a closure 29 secured in place with a snap ring 30. Theclosure 29 also serves to keep in place a flexible diaphragm 31 whichseals the reservoir 24 from contaminants outside the drill bit. Theclosure 29 has a passageway 32 in communication with the outside of thediaphragm 31 and the exterior of the drill bit so that the pressure onthe lubricant system is generally in balance.

Preferably the inside diameter of the seal 22 in its relaxed conditionbefore being installed into cutter groove 21 is larger than the outsidediameter of that portion of the shaft 14 which is operatively associated-with the seal.

Also, the outside diameter of the seal 22 in its relaxed conditionbefore being installed is larger than the maximum diameter of the cuttergroove 21.

Further, the inside diameter of the seal 22 after it has been installedinto cutter groove 21 is smaller than that portion of the shaft 14 whichis operatively associated with the seal.

For example, the maximum diameter of groove 21 may be 2.805 inches. Theoutside diameter of the seal 22 may be 2.906 inches and the insidediameter of the seal may be 2.109 inches so that dimension A of the seal22 is 0.398 inches. The diameter of the shaft 14 operating with the sealmay be 2.065 inches. This provides a diametral clearance between theseal and the shaft which is at least 1 percent of the inside diameter ofthe seal 22.

Thus, the seal 22 when installed in operating position is in radial andcircumferential or hoop compression. The inside diameter portion of thesealis also in hoop compression even though it must be pressed on theshaft 14.

The difference between the shaft diameter 2.065 inches and the groovediameter 2.805 inches is 0.740 inches in diameter or 0.370 inches fromthe top of the shaft 14 to the bottom of the groove 21. The seal 22 hasa radial extent'of 0.398 inches (dimension A). Thus, the cross sectionof the seal when installed is displaced radially 0.028 inches orapproximately seven percent.

Since the seal 22 slides on the shaft 14 when the cutter 15 is rotated,it is desirable that the seal portion in contact with the shaft have itsfibers in compression. If this portion of an elastomeric seal is intension, the seal tends to fail in fatigue forming cracks normal to thedirection of seal sliding with resultant leaks and reduced drill bit(bearing) life. It is believed that such failure occurs because anelastomeric in tension contracts when heated and the friction of therotating seal on the shaft causes heat. Also, if the seal is in tensionwhere it contacts the shaft, it is'believed that the seal tends to stickand slip on the shaft as it rotates thereon and such alternate staticand sliding condition could subject the seal to alternate tensile andcompressive stresses which may lead to fatigue failure of the seal.

As previously stated, the seal 22 of the present invention is in hoop orcircumferential compression in operation and such seals have beensuccessfully tested in the field.

While the seals tested have been made of Buna-N of approximately 70durometer, it is apparent that other elastomeric materials may be used.Also, while the seal 22 has been shown as having a generally rectangularcross section with rounded ends, any suitable shape may be used.

The seal arrangement of the invention provides a drill bit seal whichoccupies little axial space so that more bearing capacity may beprovided in the limited space available, and an improved seal whichprovides excellent fatigue characteristics.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction, may be 5 made within the scope of the appended claimswithout departing from the spirit of the invention.

What is claimed is:

1. Seal means for use in an earth boring drill bit having a head, abearing shaft arranged thereon and a cutter rotatably mounted on thebearing shaft, including:

the cutter having a circumferential groove therein,

an elastomeric seal ring in said groove,

the seal ring, the groove and the bearing shaft area confronting thegroove being sized so that upon assembly of the cutter on the shaft theseal ring is compressed less than of its relaxed condition radialthickness,

the seal ring having a radial cross-sectional extent at least one andone-half times its axial extent.

2. Seal means according to claim 1 wherein:

the inside diameter of the sealing ring being larger than the diameterof the shaft when the seal ring is in its relaxed condition before beinginstalled in the drill bit cutter.

3. Seal means according to claim 1 wherein:

the elastomers at the inside diameter and at the outside diameter of theseal ring are in hoop compression.

4. Seal means according to claim 1 wherein:

the seal ring is in hoop compression and radial compression.

5. Sealmeans according to claim 1 wherein:

the elastomer at the inside diameter of the seal ring is in hoopcompression.

6. Seal means according to claim 1 wherein:

the seal ring rotates with said cutter.

7. Seal means for use in an earth boring drill bit having a head, abearing shaft arranged thereon and a cutter rotatably mounted on thebearing shaft, including:

the cutter having a circumferential groove therein,

an elastomeric seal ring in said groove in sealing and slidingengagement with said shaft,

the inside diameter of the sealing ring being larger than the diameterof the shaft when the seal ring is in its relaxed condition before beinginstalled in the drill bit cutter.

8.v Seal means according to claim 7 wherein:

the inside diameter of the seal ring is smaller than the shaft diameterafter the seal is installed in the cutter groove.

9. Seal means for use in an earth boring drill bit having a head, abearing shaft arranged thereon and a cutter rotatably mounted on thebearing shaft including:

the cutter having a circumferential groove therein,

an elastomeric seal ring in said groove in sealing and slidingengagement with said shaft,

the diametral clearance between the outside diameter of the shaft andthe inside diameter of the seal ring in its relaxed condition beforebeing installed in the cutter groove and on said shaft, is at least onepercent of the inside diameter of the seal ring.

10. A drill bit comprising:

at least one head,

a bearing shaft arranged on said head, and

a cutter rotatably mounted on said bearing shaft,

said cutter having a circumferential groove therein,

and

and an elastomeric seal ring in said groove in sealing and slidingengagement with said shaft,

said seal ring, said groove, and said bearing shaft area confrontingsaid groove being sized so that upon assembly of said cutter on saidshaft, said seal ring is compressed less than 10 percent of its relaxedcondition radial thickness,

said seal ring having a radial cross-sectional extent at least one andone-half times its axial extent.

Patent No. 3,765m5 Dated t r-'16, 1973 Inventor(s) Henry W. Murdoch eta1.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

On the title page, change the Assignee "G. W. Murphey Industries, Inc.to G. w. Murphy Industries, Inc.

Column 2,v line 2, change "0.25" to 0.025

Signed and. sealed this 14th day of June l97)+.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. c. MARSHALL DANN Attesting Officer CommissionerofPatents FORM PO-105O (10-69) USCOMM-DC 60316-P69 i 0.5. GOVIRNMINTPRINTING OFFICE "ll 0-310-334,

1. Seal means for use in an earth boring drill bit having a head, abearing shaft arranged thereon and a cutter rotatably mounted on thebearing shaft, including: the cutter having a circumferential groovetherein, an elastomeric seal ring in said groove, the seal ring, thegroove and the bearing shaft area confronting the groovE being sized sothat upon assembly of the cutter on the shaft the seal ring iscompressed less than 10% of its relaxed condition radial thickness, theseal ring having a radial cross-sectional extent at least one andone-half times its axial extent.
 2. Seal means according to claim 1wherein: the inside diameter of the sealing ring being larger than thediameter of the shaft when the seal ring is in its relaxed conditionbefore being installed in the drill bit cutter.
 3. Seal means accordingto claim 1 wherein: the elastomers at the inside diameter and at theoutside diameter of the seal ring are in hoop compression.
 4. Seal meansaccording to claim 1 wherein: the seal ring is in hoop compression andradial compression.
 5. Seal means according to claim 1 wherein: theelastomer at the inside diameter of the seal ring is in hoopcompression.
 6. Seal means according to claim 1 wherein: the seal ringrotates with said cutter.
 7. Seal means for use in an earth boring drillbit having a head, a bearing shaft arranged thereon and a cutterrotatably mounted on the bearing shaft, including: the cutter having acircumferential groove therein, an elastomeric seal ring in said groovein sealing and sliding engagement with said shaft, the inside diameterof the sealing ring being larger than the diameter of the shaft when theseal ring is in its relaxed condition before being installed in thedrill bit cutter.
 8. Seal means according to claim 7 wherein: the insidediameter of the seal ring is smaller than the shaft diameter after theseal is installed in the cutter groove.
 9. Seal means for use in anearth boring drill bit having a head, a bearing shaft arranged thereonand a cutter rotatably mounted on the bearing shaft including: thecutter having a circumferential groove therein, an elastomeric seal ringin said groove in sealing and sliding engagement with said shaft, thediametral clearance between the outside diameter of the shaft and theinside diameter of the seal ring in its relaxed condition before beinginstalled in the cutter groove and on said shaft, is at least onepercent of the inside diameter of the seal ring.
 10. A drill bitcomprising: at least one head, a bearing shaft arranged on said head,and a cutter rotatably mounted on said bearing shaft, said cutter havinga circumferential groove therein, and an elastomeric seal ring in saidgroove in sealing and sliding engagement with said shaft, the insidediameter of said sealing ring being larger than the diameter of saidshaft when said seal ring is in its relaxed condition prior to beinginstalled in said cutter.
 11. A drill bit comprising: at least one head,bearing shaft arranged on said head, and a cutter rotatably mounted onsaid bearing shaft, said cutter having circumferential groove therein,and an elastomeric seal ring in said groove in sealing and slidingengagement with said shaft, said seal ring, said groove, and saidbearing shaft area confronting said groove being sized so that uponassembly of said cutter on said shaft, said seal ring is compressed lessthan 10 percent of its relaxed condition radial thickness, said sealring having a radial cross-sectional extent at least one and one-halftimes its axial extent.